(1) Field of the Invention
The present invention relates to a semiconductor memory, more particularly, to a dual port type semiconductor memory using a dynamic type random access memory (RAM) advantageously in a memory of a computer system.
(2) Description of the Prior Art
Recent research and development in the field of semiconductor memories have concentrated on the achievement of greater miniaturization and integration. Few studies, however, have been made on the achievement of greater efficiency of utilization of semiconductor memories.
One well-known technique for achieving greater efficiency of utilization of semiconductor memories is the use of a dual port type semiconductor memory using a static type RAM.
A static type RAM has the feature of "non-destructive read out". That is to say, even if data is read out from a memory cell, the data stored in the memory cell is not erased. Since the static type RAM has the feature as mentioned above, it is possible to simultaneously read out two data from the same memory cell.
A static type RAM, however, has many elements compared with a dynamic type RAM, usually six as opposed to two. Therefore, a static type RAM is disadvantageous in miniaturizing memories and increasing therefore their integration.
In this sense, a dynamic type RAM is advantageous. However, no dynamic type RAM having a single transistor memory cell offers "non-destructive read out". This means that once data is read out from a memory cell, the data in the memory cell is erased. No dual port type semiconductor memory using a dynamic type RAM has therefore been realized up to now.